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Heater Pressure Switch Error

Fix FLO, PS, and LO error codes from flow detection problems

Flow Issues
80% of Errors
20+ GPM
Min Required
Safety
Shutdown
$150-400
Repair Cost

Quick Answer

Pressure switch errors (FLO, PS, LO codes) occur when the heater detects insufficient water flow. In 80% of cases, the problem is actual low flow from dirty filters, closed valves, or low pump speed - not a faulty switch. Clean your filter first, ensure all valves are open, and run pump on high speed. If error persists, the pressure switch may need cleaning or replacement.

Understanding Heater Pressure Switches

How Pressure Switches Work

  • Flow detection: Senses water movement through heater
  • Pressure differential: Measures pressure change with flow
  • Safety shutoff: Prevents operation without water
  • Electrical contact: Opens/closes circuit to control
  • Adjustable settings: Calibrated for minimum flow

Why Flow Detection Matters

  • Heat removal: Water carries heat away from exchanger
  • Prevents damage: No flow = instant overheating
  • Efficiency: Proper flow ensures heat transfer
  • Safety: Prevents steam, boiling, explosions
  • Warranty: Required for coverage validity

Critical Safety: Never bypass or jumper a pressure switch. Operating without flow detection can crack heat exchangers, create steam explosions, or cause fires within minutes.

Pressure Switch Error Codes by Brand

Common Error Displays

  • FLO: Generic flow error (most brands)
  • PS: Pressure switch open
  • LO: Low flow detected
  • E06: Flow sensor fault (Pentair)
  • FLS: Flow switch stuck
  • PRS: Pressure switch error (Raypak)

Error Behavior

  • • Heater won't start at all
  • • Starts then shuts down immediately
  • • Intermittent operation
  • • Error appears with pump running
  • • Clears temporarily then returns
  • • Multiple errors displayed

Southlake, Westlake, Grapevine Tip: During spring pollen season, clogged filters cause frequent pressure switch errors. Check filter pressure first before assuming switch failure.

Real Flow Problems (80%) vs. Switch Failure (20%)

Common Flow Restrictions - Check These First!

Filtration Issues:

  • Dirty filter: #1 cause - clean when pressure rises 8-10 PSI
  • Old filter media: Sand channels, cartridge collapsed
  • Undersized filter: Can't handle flow requirements
  • Multiport valve issues: Internal problems restrict flow

Pump & Plumbing:

  • Low pump speed: Variable speed set too low
  • Clogged baskets: Pump/skimmer baskets full
  • Closed valves: Bypass or return valves partially shut
  • Air leaks: Suction side air reduces flow

Quick Test: If error clears when you clean filter or open valves, the pressure switch is working correctly - you had a flow problem.

Actual Pressure Switch Failures

Mechanical Failures:

  • • Stuck diaphragm from debris
  • • Corroded electrical contacts
  • • Cracked switch housing
  • • Adjustment screw drift
  • • Spring tension loss

Symptoms of Bad Switch:

  • • Error with obvious good flow
  • • No clicking sound when flow changes
  • • Intermittent errors randomly
  • • Works after tapping switch
  • • Visible damage or leaking

Age Factor: Pressure switches typically last 5-8 years. Frequent cycling from variable speed pumps may shorten lifespan.

DIY Troubleshooting Steps

Step 1: Verify Actual Flow

  1. Check filter pressure gauge (should be under 25 PSI)
  2. Feel return jets for strong flow
  3. Ensure pump is on high speed
  4. Open all valves completely
  5. Clean pump and skimmer baskets

Step 2: Basic Switch Tests

  1. Turn pump off and on - listen for switch click
  2. Gently tap switch housing with screwdriver handle
  3. Check for loose wire connections
  4. Look for corrosion or water damage
  5. Verify switch is mounted securely

Step 3: Flow Optimization

  1. Clean filter if pressure is high
  2. Check for air bubbles in pump
  3. Verify heater isolation valves are open
  4. Test with spa mode if available (higher flow)
  5. Remove any flow restrictions

Success Rate: 80% of pressure switch errors are resolved by cleaning filters and ensuring proper flow. Only 20% require switch replacement.

Pressure Switch Safety Warnings

  • Never bypass or jumper out a pressure switch - severe damage occurs within minutes
  • Do not operate heater if switch is suspected faulty - overheating risk
  • Electrical testing of switches requires proper tools and knowledge
  • Incorrect switch replacement can void warranty and create hazards
  • Low flow operation damages heat exchangers beyond repair
  • Always verify actual water flow before condemning switch

Variable Speed Pump Considerations

Special Issues with VS Pumps

Common Problems:

  • • Low speed settings don't meet heater flow requirements
  • • Programmed speeds change without heater consideration
  • • Ramp-up time too slow for switch activation
  • • Energy-saving modes conflict with heating needs

Solutions:

  • • Set minimum 2400 RPM for heater operation
  • • Program "heater mode" at high speed
  • • Use external relay to force high speed
  • • Adjust ramp rates for quick flow establishment

Pro Tip: Many VS pump flow errors are solved by creating a dedicated heater speed setting that automatically runs when heat is called for.

Professional Pressure Switch Diagnosis

1

Verify Actual Water Flow

Confirm water is flowing before troubleshooting switch

⚠️ Warning: Most pressure switch errors are caused by actual low flow, not switch failure

2

Inspect Pressure Switch Location

Check switch mounting and connections

⚠️ Warning: Never bypass pressure switch - it prevents heater damage from low flow

3

Test Switch Mechanically

Basic tests to verify switch operation

⚠️ Warning: Electrical testing requires voltmeter and safety knowledge

4

Clean Sensing Ports

Remove debris that may affect pressure sensing

⚠️ Warning: Some switches have sealed diaphragms that cannot be cleaned

5

Evaluate Flow Rate Requirements

Ensure system meets heater specifications

⚠️ Warning: Undersized pumps or plumbing cause chronic pressure switch errors

6

Professional Electrical Testing

Advanced diagnosis and replacement

⚠️ Warning: Incorrect switch replacement can damage heater or create safety hazards

Pressure Switch Error Repair Costs

🔧 DIY Attempt

Estimated Cost:$0-50
Time Required:1-2 hours
Difficulty:Moderate

⚠️ Risks:

  • Misdiagnosing flow problems as switch failures
  • Damaging switch with improper cleaning attempts
  • Creating electrical hazards with connection work
  • Missing underlying flow system problems
  • Voiding warranty with incorrect troubleshooting

👷 Professional Service

Service Cost:$150-400
Completion Time:Same day service

✅ Includes:

  • Complete flow system evaluation
  • Pressure switch testing and adjustment
  • Flow rate measurement and optimization
  • Switch cleaning or replacement if needed
  • Pump programming for proper heater flow
  • System validation and warranty

Detailed Cost Breakdown

Item/ServiceLowHigh
Diagnostic service call$125$200
Flow system optimization$150$250
Pressure switch replacement$200$400
Switch adjustment only$150$200
VS pump programming$100$150
Total Range$725$1200

💰 Value Tip: CoOpPools offers transparent pricing with no hidden fees. Our worker-owned model means fair prices and invested service.

Prevention Tips

1

Maintain Proper Filter Cleaning Schedule

Clean filter when pressure rises 8-10 PSI above clean starting pressure. High filter pressure is the #1 cause of flow errors.

Homeowner Friendly
2

Run Pump at Proper Speed

Ensure pump runs at high speed during heating cycles. Variable speed pumps must deliver 20+ GPM for heater operation.

Some Experience Needed
3

Annual Flow System Check

Professional inspection of pump performance, filter condition, and plumbing restrictions prevents flow-related shutdowns.

👷Professional Recommended
4

Keep Baskets Clean

Empty pump and skimmer baskets weekly. Clogged baskets restrict flow triggering pressure switch errors.

Homeowner Friendly
5

Monitor System Pressure

Install pressure gauges before and after heater. Early detection of flow problems prevents switch damage.

Some Experience Needed

🏊 Pro Tip: Regular professional maintenance prevents 90% of pool problems.Get your maintenance quote today

This Issue Requires Professional Service

Pressure switch errors prevent heating and often indicate flow problems that can damage equipment. Our technicians diagnose whether you have actual flow issues or switch failure, optimizing your system for reliable heater operation.

Mention "pressure switch errors" when calling for faster service

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💡 Did You Know? Pool problems often occur together.heater-pressure-switch-error can lead to or be caused by these related issues. Understanding the connections helps prevent future problems.